In the process of manufacturing aluminum alloy wheels, the procedure of detecting airtightness is indispensable, which is directly related to driving safety. Therefore, manufacturers attach great importance to airtightness detecting procedure. Traditional methods for detecting airtightness include both airtightness detecting by water and airtightness detecting by helium gas. However, manufacturers presently use water airtightness machines without any wheel centering device, with the position of wheels being roughly determined only by human eyes. When the conical upper seal presses downward, it has to be inclined to seal the front rim of the wheel tightly, which is extremely apt to wear the equipment. In addition, the traditional water airtightness machines possess no function of rotating the wheel upon detection, making it impossible to conveniently and visually judge whether there is leak at any circumferential position of the wheel.